(a) Field of the Invention
This invention relates to a system for suspending cable wires from a building structure and more particularly, but not by way of limitation, to a system for holding a plurality low voltage data and telecommunication cables held tightly together and suspending them from a suspension wire secured to the building structure.
(b) Discussion of Known Art
With the increased use of information processing equipment by society, there has been a rapidly increasing need to provide buildings with the necessary infrastructure to allow the occupants of a building the ability to take full advantage of available telecommunication and data transfer technology. Organizations will typically provide their employees with computers and other data processing equipment connected to mainframes, servers, and other data processing and communications equipment that is housed in the building or at a remote site. The installation and use of this equipment has made it necessary to install extensive data transfer cabling and wiring. This cabling is typically low voltage cable or fiber optic cable, which must be installed throughout the building. In the past, individual low voltage computer cables and wiring used for data communications networking, such as those used with a computer mainframe, servers and the like, have been threaded loosely together in walls and ceiling plenums of buildings. In situations where a large number of these cables are to be installed, the well known solution has been to install cable trays or ladder racks for carrying these cables throughout the building.
For small installations, the data transfer cables are typically simply routed through the plenum areas in ceilings or through crevasses between the building's walls. These installations simply route the cable over and around the building's existing systems and structure, often making contact with many of these installations. This type of installation gives little regard to the importance of placing the cables away from metallic structures that may build up electrical charges; electrical devices such as lights and motors; of holding the cables together as a unit for improved protection of the cable's insulation to avoid cold flow; and maintenance and inspection of the cables by the user. For installations with a large number of cables, the solution of installing a cable tray or electrical conduit for providing a system for support and routing has been the only reliable solution. However, cable trays are expensive to purchase and even more expensive to install. A typical installation of cable tray carries an average cost of five dollars per foot, making elaborate installations through large buildings extremely expensive. Moreover, cable trays are fairly large and require significant mounting structure and space within the building. Often, where installations are to be made in existing structures, the existing heating and air conditioning systems, sprinkler systems and electrical systems, must be avoided in order to prevent physical or electrical interference with the cable plant.
Electrical conduits are typically used in applications where a smaller quantity of cabling is to be installed. However, electrical conduit is also very expensive, costing on average about three dollars per foot to install. Moreover, conduit is further disadvantaged in that it typically does not allow visual inspection of the cabling contained therein, and suffers from a limited availability of space within the conduit. Another disadvantage of conduit is that a user's system may easily outgrow the carrying capabilities of the conduit, making it necessary to overhaul the entire system. Still another disadvantage is that if additional cabling needs to be added, and the conduit has space available for this cabling, then the cable must be pulled through the conduit, risking damage to the insulation and the cable itself.
For example, a high frequency telecommunications cable known as Electronic Industry Association/Telecommunications Industry Association (EIA/TIA) standard Category 5 or Underwriter's Laboratory (UL) Level 5 cable only allows for twenty five (25) pounds of tensile pull. If one exceeds this load one runs a serious risk of altering the capacitance of the cable. If the structural integrity of the cable is damaged, excessive attenuation and near-end crosstalk can also occur. Binding can occur when a cable is pulled tightly around a sharp object such as a support beam, hanging ceiling hardware, or ventilation equipment. Damage to the cable can range from a slight flattening of the cable pairs to complete sheath destruction and removal of individual conductor insulation (a symptom known as "a shiner"). These conditions cause the cable to test out of tolerance as specified by the EIA/TIA 568A and TSB 67 Standards.
Until recently, high speed data transfer systems were not widely available, therefore little emphasis has been placed on the protection of cables from extreme temperature changes and interference from surrounding electrical charges. This is largely due to the fact that conventional cables can easily transfer data for systems using data transfer speeds less than 10 megabits or 16 megahertz.
As the speed of data systems increases the demands on the performance of the cabling systems used to interconnect these systems increases. This is due to the fact that as the speed increases, the size of the pulses representing data get smaller. Small voltage pulses from, say, static charges or from installations within the plenums of the building can easily mimic real information pulses. Thus, care must be taken to ensure that the possibility of interference from these external sources be reduced in order to preserve the size, number, and shape of the information pulses being transmitted, so that receiving equipment can correctly interpret the information being conveyed.
The increased tolerance requirements of information cabling has prompted the introduction of more stringent standards. The requirements of the NEC EIA/TIA 568A Standards and TSB 67 Testing Criteria establish standard methods of cable support, bend radii of cable lines, linear installation support and cable routing in order to assure safe, reliable installations. These standards also include stricter cable protection and installation standards and testing criteria are essential for the proper operation of modern high speed networks.
It is not uncommon to find installations for 100 megabit and ATM (Asynchronous Transfer Mode) 155 megabit operation. These high speed systems require the use and availability of well insulated cabling which, as indicated earlier, is widely known as EIA/TIA Category 5 voice and data cabling systems. The expense and performance criteria imposed by these cable systems and high speed fiber optic systems has prompted telecommunications cabling manufacturers and systems installations experts to recognize a serious need for a cabling suspension system for ceilings and plenum areas in business, government and academic office environments, warehouses, plants, and training facilities.
New high speed cabling systems must be installed to insure that each cable run passes the stricter National Electric Code (NEC) standards, EIA/TIA 568A Standards and TSB 67 Testing Criteria. As stated earlier, cable support, bend radius, linearity of installation and cable protection are important factors that must now be addressed in order to pass the stricter installation and testing criteria. The sensitivity of high speed circuits to irregularities in the physical media (cable) caused by kinking, stretching, binding and general rough handling is very important. Also it is recognized that precise routing and even tight bundling of cable should be carefully controlled because these factors affect the integrity of the data being transferred. Thus, the installation should be placed away from sources of electromagnetic interference and radio frequency interference.
The problems associated with the support of cable has found many additional approaches, for example in U.S. Pat. No. 2,470,840 to Hain and U.S. Pat. No. 2,515,603 to Kaplan, electrical cable supports having split grommets or bushings are shown for holding a portion of a cable.
In U.S. Pat. Nos. 809,993 to Sorg, 1,164,613 to Jewell, 1,725,120 to Williams, 1,832,996 to Percival et al. and 4,973,259 different types of clamps or brackets are described for holding cable or wire and suspended from another parallel cable or conduit. Similarly, in U.S. Pat. No. 5,443,232 to Kesinger et al. an apparatus for hanging TV cable and the like is described using support brackets with rubber grommets for receiving a portion of coaxial cable therein.
The stricter standards and more stringent performance criteria of telecommunications cabling and fiber optic systems no longer permits simple weaving of the data transmission media through the plenum areas of buildings. However, none of the known prior art provides a reliable, inexpensive, easy to install, systems that can meet the strict performance criteria imposed by modern high speed data transfer systems. Moreover, the cost and physical requirements of installing cable trays and electrical conduit has imposed a heavy burden on those who wish to take advantage of the advancements offered by modern high speed data systems.
Thus there remains a need for a highly reliable, simple, and inexpensive system for installing and suspending telecommunications and data transfer cabling in buildings. Moreover, due to the need to avoid physical and electrical obstacles in a structure, there remains a need for a simple data cabling support system that allows precise placement of cable to be routed through buildings. Still further, there remains a need for a system that will reduce the risk of damage to the cabling being installed. Still further, there remains a need for a cabling support system that can be easily mastered by field personnel, and thus producing inexpensive, high quality, reliable installations of data transfer systems.